WESTCHESTER, N.Y. -- Investigations into what caused the deadly explosion in Harlem Wednesday could take up to three weeks, according to Con Edison.

Crews from Con Ed are currently on the scene working with Fire Department officials and other government agencies to find out what caused the explosion that leveled two buildings and left eight people dead and several others still missing. Con Ed spokesperson Sidney Alvarez said that they have not yet officially determined the cause of the explosion.

"We treated it as if it were a gas leak, because that allows us to take extreme precaution when going in," Alvarez said. "But the official word on what caused it could take up to three weeks."

The odor of gas had been detected near the scene prior to the explosion. Con Ed received a report at 9:13 a.m. from a resident of nearby 1652 Park Ave. who reported smelling gas inside that apartment building. The resident indicated that the odor may have been coming from outside the building. Crews were dispatched at 9:15 a.m. and were on their way when the explosion occurred at 9:31 a.m.

About 75 Con Ed personnel were sent to the scene following the explosion. All electric and gas service was shut down between East 116th and East 117th Streets on the west side of Park Avenue, as well as on the north side of East 116th Street near Park Avenue.

Con Ed inspects its 4,300-mile network of gas mains at least once per year using mobile gas detection vehicles. The last mobile survey on Park Avenue between 116th and 117th Streets was on Feb. 28 and found no leaks in the block, according to Con Ed.

The company has conducted reviews of all gas odor complaints on the block in the last three years and all gas main work done in the last 10 years. There was a gas odor complaint at 1644 Park Ave. on May 17, 2013, which involved problems on the customers equipment. Repairs were made by a contractor and Con Ed reconnected the line on July 3. There was a gas leak reported on the west side of the street on July 22, 2010, which involved a faulty valve on a customer's stove.

Con Ed replaced 69 feet of gas main in December 2011 in connection with a customer's installation of a new water service line. In July 2004 the company made a routine repair to the gas main to seal a gas leak on the block.